1. Field of the Invention
This invention relates to a method for cleaning semiconductor devices and wafers processed by thermal gradient zone melting.
2. Description of the Prior Art
The recent introduction of thermal gradient zone melting processing (TGZM) as a new commercial manufacturing tool for making semiconductor devices has also introduced new problems on occasions. The most useful application of TGZM is to migrate aluminum "wires" through silicon wafers to produce planar electrical isolation regions. The regions protect the integrity of the electrical characteristics of individual devices. Additionally, the regions have sufficient width to enable one to laser scribe the wafer and divide or dice, the wafer into individual devices for further processing and encapsulation.
However, the molten aluminum during the process reacts with air of the ambient in the apparatus, the silicon of the wafer, the adjacent silicon oxide of the mask employed in TGZM and forms a film reaction product which appear to be mullite, carborundum and mixtures thereof on the surfaces of the wafer as well as on the oxide layer. These reaction products inhibit further processing of the wafers and devices. In some instances, the presence of the reaction products has only an aesthetic effect. In other instances, the reaction products prevent the removal of portions of the oxide layer or prevents further processing of exposed surfaces of the silicon wafer.
Conventional means embodying known etching solutions employed in cleaning and etching silicon semiconductor material have proven to be unsuccessful in removing the reaction products. Aqua regia, phosphoric acid, bromine in methanol, and the like, fail to remove the reaction products. Mullite, in particular, is resistant to all acid and alkali etches with the exception of hydrofluoric acid which only very slowly attacks mullite. The use of a hydrofluoric acid etch is undesirable since this acid also removes the silicon oxide mask on the wafer and because the required reaction time is excessive.
Potassium hydroxide is a known etchant for selective etching of silicon but is most useful with the (100) geometry. The effect on the (111) geometry is very slight.
It is therefore an object of this invention to provide a new and improved method for removing the reaction products which result from migrating aluminum through silicon by thermal gradient zone melting which overcomes the deficiencies of the prior art.
Another object of this invention is to provide a new and improved etching solution of potassium hydroxide for removing the reaction products produced by the migration of aluminum through silicon by thermal gradient zone melting.
Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter.